In a stationary antenna and receiver, the antenna boresight is mechanically pointed at a communications transmitter source. As an example, in a Direct Broadcast Satellite (DBS) TV service having a receiver terminal with an 18 inch parabolic dish antenna, the antenna is pointed by mechanical means at a geostationary broadcasting satellite.
In a mobile antenna-receiver, a phased array technique is commonly employed such that the phased array is used to maintain the receive antenna beam pointing at a broadcast source while the antenna-receiver platform is rotated. Since the platform typically has pitch, roll, and heading variations that change with time, rapid pointing angle changes are necessary capabilities required of the communications antenna-receiver. Thus, relatively high bandwidth tracking mechanisms are required to maintain instantaneous beam pointing. Further, a communications link start-up requires that the antenna-receiver subsystem have mechanisms to search the volume of space where the desired source may be located, and acquire an angular position of the source relative to the mobile platform.
One current system known as a smart antenna exploits space selectivity. “Smart-Antenna Systems for Mobile Communications Networks” by Bellofiore, et. al., IEEE Antenna's and Propagation Magazine, Vol. 44, No. 3. Signal processing aspects of the smart antenna has concentrated on the development of efficient algorithms for direction-of arrival (DOA) estimation and adaptive beam forming. After the digital signal processor receives the time delays from each antenna element, it computes the DOA of the signal of interest. The excitations (the amplitudes and phases of the signals) are then adjusted to produce a radiation pattern that focuses on the signal of interest, while turning out any signal not of interest. One smart antenna system utilizes adaptive array systems. After the system down converts the received signal to baseband and digitizes them, the signal of interest is located using the DOA algorithm. The signal of interest and signals not of interest are continuously tracked by dynamically changing the weights (amplitudes and phases). However, adaptive array systems are digital processing intensive. For example, by employing numerous elements to steer the nulls to the signals not of interest, signal processing loads are increased and hence system cost.